The invention relates to internal combustion engines of the kind in which the movement of fluids is controlled by poppet valves. The opening of the valves is effected by rotating cams, generally via associated parts such as tappets, push rods and rockers, against the action of strong valve springs which urge the valves towards and close them against their respective valve seats.
Due to thermal expansion of the valves and other parts of the engine, a certain clearance gap has to be provided in each chain of valve actuating mechanism between a cam surface and the end of the stem of the valve actuated thereby in order to ensure that the valve can be firmly closed against its valve seat during the appropriate period of the engine cycle. Failure of a valve to close fully not only results in bad engine performance but also in burning of the valve and its seat, and atmospheric pollution above prescribed limits. Any excess clearance leads to an undesirable tapping noise, and consequently the clearance gap is normally adjusted within a range which ensures proper valve closure under the various operating conditions of the engine while maintaining the noise as low as possible in the circumstances. However, due to wear which occurs between the valve and its seat and between the engaging surfaces of the chain of valve mechanism from the cam surface to the valve stem, which can either increase or decrease the said clearance gap depending upon the conditions of engine operation, the clearance gap has to be adjusted several times during the life of the engine. Some engines are equipped with self-adjusting hydraulic tappets for automatically adjusting the clearance, engine oil pressure causing the tappets to lengthen and automatically take up the clearance during engine operation, but with most engines re-adjustment of the clearance gap has to be effected manually from time to time.
The reduction of the clearance due to wear between the valve and its seat is of critical importance, and while it is offset to some extent by the wear between the engaging surfaces of the valve actuating mechanism, it remains a serious problem. The use of lead-less gasoline to reduce pollution has accelerated wear between the valve and its seat which, where it is not possible to incorporate hydraulic tappets, has had to be slowed down by expensive means, such as sodium-cooled valves, in an attempt to avoid clearance gap adjustment being necessary more frequently than the permissible interval between maintenance of other parts of the vehicle, which intervals continue to become longer by the use of improved materials and mechanical design.
Various valve-actuating arrangements incorporating mechanical springs or expansion compensating devices have been proposed or used during the last half century for reducing or silencing tappet noise. Examples of such arrangements are described in U.S. Pat. No. 1,613,117 of J. C. Miller issued Jan. 4, 1927, U.S. Pat. No. 1,692,435 of A. Clemensen issued Nov. 20, 1928, U.K. Pat. No. 305,522 of A. H. F. Perl, U.S. Pat. No. 2,225,265 of G. M. Fitts issued Dec. 17, 1940 and U.S. Pat. No. 3,183,901 of N. C. Thuesen issued May 18, 1965.
To the best of applicant's knowledge and belief, the problem faced by automobile manufacturers of maintaining atmospheric pollution from exhaust gases below prescribed limits over a specified interval of operation, and without interim valve clearance adjustment, has not hitherto been solved by an inexpensive mechanical spring system which is simple to fabricate and can be incorporated easily in existing or new engine designs.